1. Field of the Invention
The present invention generally relates to a sheet finishing device and an image forming apparatus and particularly relates to a compact sheet finishing device that can be installed inside an image forming apparatus.
2. Description of the Related Art
Japanese Patent Application Laid-open No. 2006-168860 discloses a combination of an image forming apparatus and a sheet finishing device that performs finishing processing such as sheet sorting or stapling on sheets output from the image forming apparatus. The sheet finishing device can be detachably attached to the image forming apparatus that can be a copying apparatus, a facsimile apparatus, or a multifunction product (MFP) having copying and facsimileing functions.
More particularly, the sheet finishing device is attached to an outer side surface of the image forming apparatus. Moreover, a collecting tray is provided on an outer side surface of the sheet finishing device. However, this arrangement increases the combined installation area of the image forming apparatus.
Japanese Patent No. 3571986 and Japanese Patent No. 3667211 each discloses an image forming apparatus in which a sheet finishing device is installed inside the main body of the image forming apparatus. This arrangement enables reduction in the installation area of the image forming apparatus.
In the configuration disclosed in Japanese Patent No. 3571986, the sheet finishing device is installed in a space between an image forming unit and an image reading unit of the image forming apparatus. This arrangement enables suppressing increase of the height the image forming apparatus. To enable proper installation of the sheet finishing device in that particular space, the sheet finishing device is provided with following units. That is, the sheet finishing device is provided with an aligning unit that collects recording sheets one by one from the image forming unit in the direction parallel to a conveying direction of the recording sheets and aligns the rear ends of the recording sheets, a stapling unit that staples the recording sheets aligned by the aligned unit to obtain a sheet stack, and a collecting tray for stacking the sheet stack stapled by the stapling unit or the recording sheets conveyed from the aligning unit.
The collecting tray is rotatably attached by a base member at the downstream side of a conveying direction of the sheet stack. A front portion of the collecting tray situated at the upstream side of the conveying direction is biased with a spring such that the front portion moves according to the number of recording sheets in the sheet stack.
In the configuration disclosed in Japanese Patent No. 3667211 the sheet finishing device is installed in a space between an image forming unit and an image reading unit of the image forming apparatus. This arrangement enables suppressing increase of the height the image forming apparatus. The sheet finishing device also includes an aligning unit that collects recording sheets conveyed one by one from the image forming unit in the direction parallel to a conveying direction of the recording sheets and aligns the rear ends of the recording sheets, a stapling unit that staples the recording sheets aligned by the aligned unit to obtain a sheet stack, and a collecting tray for stacking the sheet stack stapled by the stapling unit or the recording sheets conveyed from the aligning unit.
In the sheet finishing device disclosed in Japanese Patent No. 3571986, the aligning unit has a sheet supporting surface that is inclined with respect to the conveying direction. The recording sheets conveyed to the aligning unit are collected on the sheet supporting surface and the weight of the collected recording sheets pushes the rear ends thereof to abut against rear end referencing members of the aligning unit for alignment and positioning. For such a configuration to work, the sheet supporting surface needs to be inclined by an angle that is large enough to make the recording sheets slide down toward the rear end referencing members. That increases the height of the aligning unit thereby putting limitations on the height reduction of the image forming apparatus.
In the sheet finishing device disclosed in Japanese Patent No. 3667211, a sheet supporting surface of the aligning unit lies substantially parallel to the conveying direction of the recording sheets. On the one hand, that allows reduction in the height of the aligning unit. However, on the other hand, alignment and positioning of the recording sheets at rear end referencing members remains inadequate. This problem is described below with reference to FIG. 12.
FIG. 12 is a schematic diagram for explaining the relation between a collecting tray 3 and rear end referencing members 2b of an aligning unit 2 in a sheet finishing device 1 disclosed in Japanese Patent No. 3667211. A conveying roller 4 conveys image-recorded sheets S that are output from an image forming unit (not shown) into the sheet finishing device 1. A reverse conveying member (not shown) reverses the image-recorded sheets S so that rear ends Sb thereof becomes front ends Sa and conveys the reversed image-recorded sheets S to the aligning unit 2. The image-recorded sheets S rest on a supporting surface 3a of the collecting tray 3 and a supporting surface 2a of the aligning unit 2. A level difference H between the supporting surfaces 3a and 2a causes the rear ends Sb of the image-recorded sheets S to abut against the rear end referencing members 2b of the aligning unit 2 for alignment and positioning.
A stapling unit (not shown) staples the aligned rear ends Sb to form a sheet stack of the image-recorded sheets S. The sheet stack drops along an inclined surface 3b and rests at a regulating fence 3d that is formed at the end of a bottom portion 3c having a level difference A from the supporting surface 2a of the aligning unit 2. To enable collection of the sheet stack in the collecting tray 3 in the abovementioned manner, the level difference A is maintained between the bottom portion 3c of the collecting tray 3 and the supporting surface 2a of the aligning unit 2 and a space D is maintained between the supporting surface 3a of the collecting tray and the supporting surface 2a of the aligning unit 2.
However, consider a case when the collected image-recorded sheets S that are shorter in length than a length L0 from the rear end referencing members 2b to the supporting surface 3a in the collecting tray 3 are aligned and positioned at the rear end referencing members 2b. Then, as shown in FIG. 12, because a length L1 from the rear end referencing members 2b to an end edge 2a1 of the supporting surface 2a is shorter than the length of the image-recorded sheets S, the front ends Sa of the image-recorded sheets S hang loose in the space D and the image-recorded sheets S move due to the weight of the hanging front ends Sa. That causes a misalignment Z in the rear ends Sb of the image-recorded sheets S having been aligned at the rear end referencing members 2b. As a result, it becomes likely that stapling is performed with the rear ends Sb out of alignment.